msgpack: support tzoffset in datetime

Support non-zero tzoffset in datetime extended type. If tzoffset and
tzindex are not specified, return object with timezone-naive
pandas.Timestamp internals. If tzoffset is specified, return object with
timezone-aware pandas.Timestamp with pytz.FixedOffset [1] timezone info.
pytz module is already a dependency of pandas, but this patch adds it as
a requirement just in case something will change in the future.

pandas >= 1.0.0 restriction was added to ensure that Timestamp.tz()
setter is disabled.

1. https://pypi.org/project/pytz/

Part of #204

Author: DifferentialOrange

Diff for: CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Decimal type support (#203).
 - UUID type support (#202).
 - Datetime type support and tarantool.Datetime type (#204).
+- Offset in datetime type support (#204).
 
 ### Changed
 - Bump msgpack requirement to 1.0.4 (PR #223).

Diff for: requirements.txt

@@ -1,2 +1,3 @@
 msgpack>=1.0.4
-pandas
+pandas>=1.0.0
+pytz

Diff for: tarantool/msgpack_ext/types/datetime.py

@@ -1,4 +1,5 @@
 import pandas
+import pytz
 
 # https://www.tarantool.io/ru/doc/latest/dev_guide/internals/msgpack_extensions/#the-datetime-type
 #
@@ -39,7 +40,16 @@
 BYTEORDER = 'little'
 
 NSEC_IN_SEC = 1000000000
+SEC_IN_MIN = 60
+MIN_IN_DAY = 60 * 24
 
+def compute_offset(dt):
+    if dt.tz is None:
+        return 0
+
+    utc_offset = dt.tz.utcoffset(dt)
+    # There is no precision loss since pytz.FixedOffset is in minutes
+    return utc_offset.days * MIN_IN_DAY + utc_offset.seconds // SEC_IN_MIN
 
 def get_bytes_as_int(data, cursor, size):
     part = data[cursor:cursor + size]
@@ -61,22 +71,35 @@ def msgpack_decode(data):
         tzoffset = 0
         tzindex = 0
 
-    if (tzoffset != 0) or (tzindex != 0):
-        raise NotImplementedError
-
     total_nsec = seconds * NSEC_IN_SEC + nsec
 
-    dt = pandas.to_datetime(total_nsec, unit='ns')
+    if (tzindex != 0):
+        raise NotImplementedError
+    elif (tzoffset != 0):
+        tzinfo = pytz.FixedOffset(tzoffset)
+        dt = pandas.to_datetime(total_nsec, unit='ns').replace(tzinfo=pytz.utc).tz_convert(tzinfo)
+    else:
+        # return timezone-naive pandas.Timestamp
+        dt = pandas.to_datetime(total_nsec, unit='ns')
+
     return dt, tzoffset, tzindex
 
 class Datetime(pandas.Timestamp):
     def __new__(cls, *args, **kwargs):
-        if len(args) > 0 and isinstance(args[0], bytes):
-            dt, tzoffset, tzindex = msgpack_decode(args[0])
-        else:
+        dt = None
+        if len(args) > 0:
+            if isinstance(args[0], bytes):
+                dt, tzoffset, tzindex = msgpack_decode(args[0])
+            elif isinstance(args[0], Datetime):
+                dt = pandas.Timestamp.__new__(cls, *args, **kwargs)
+                tzoffset = args[0].tarantool_tzoffset
+
+        if dt is None:
             dt = super().__new__(cls, *args, **kwargs)
+            tzoffset = compute_offset(dt)
 
         dt.__class__ = cls
+        dt.tarantool_tzoffset = tzoffset
         return dt
 
     def msgpack_encode(self):
@@ -85,6 +108,11 @@ def msgpack_encode(self):
         tzoffset = 0
         tzindex = 0
 
+        if isinstance(self, Datetime):
+            tzoffset = self.tarantool_tzoffset
+        else:
+            tzoffset = compute_offset(self)
+
         buf = get_int_as_bytes(seconds, SECONDS_SIZE_BYTES)
 
         if (nsec != 0) or (tzoffset != 0) or (tzindex != 0):
@@ -93,3 +121,19 @@ def msgpack_encode(self):
             buf = buf + get_int_as_bytes(tzindex, TZINDEX_SIZE_BYTES)
 
         return buf
+
+    def replace(self, *args, **kwargs):
+        dt = super().replace(*args, **kwargs)
+        return Datetime(dt)
+
+    def astimezone(self, *args, **kwargs):
+        dt = super().astimezone(*args, **kwargs)
+        return Datetime(dt)
+
+    def tz_convert(self, *args, **kwargs):
+        dt = super().tz_convert(*args, **kwargs)
+        return Datetime(dt)
+
+    def tz_localize(self, *args, **kwargs):
+        dt = super().tz_localize(*args, **kwargs)
+        return Datetime(dt)

Diff for: test/suites/test_msgpack_ext.py

@@ -10,6 +10,7 @@
 import warnings
 import tarantool
 import pandas
+import pytz
 
 from tarantool.msgpack_ext.packer import default as packer_default
 from tarantool.msgpack_ext.unpacker import ext_hook as unpacker_ext_hook
@@ -559,6 +560,62 @@ def test_UUID_tarantool_encode(self):
             'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
                          r"nsec=308543321})",
         },
+        'datetime_with_positive_offset': {
+            'python': tarantool.Datetime(year=2022, month=8, day=31, hour=18, minute=7, second=54,
+                                         microsecond=308543, nanosecond=321,
+                                         tzinfo=pytz.FixedOffset(180)),
+            'msgpack': (b'\x4a\x79\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xb4\x00\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=180})",
+        },
+        'datetime_with_negative_offset': {
+            'python': tarantool.Datetime(year=2022, month=8, day=31, hour=18, minute=7, second=54,
+                                         microsecond=308543, nanosecond=321,
+                                         tzinfo=pytz.FixedOffset(-60)),
+            'msgpack': (b'\x8a\xb1\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xc4\xff\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=-60})",
+        },
+        'pandas_timestamp_with_positive_offset': {
+            'python': pandas.Timestamp(year=2022, month=8, day=31, hour=18, minute=7, second=54,
+                                       microsecond=308543, nanosecond=321,
+                                       tzinfo=pytz.FixedOffset(180)),
+            'msgpack': (b'\x4a\x79\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xb4\x00\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=180})",
+        },
+        'pandas_timestamp_with_negative_offset': {
+            'python': pandas.Timestamp(year=2022, month=8, day=31, hour=18, minute=7, second=54,
+                                       microsecond=308543, nanosecond=321,
+                                       tzinfo=pytz.FixedOffset(-60)),
+            'msgpack': (b'\x8a\xb1\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xc4\xff\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=-60})",
+        },
+        'datetime_offset_replace': {
+            'python': tarantool.Datetime(year=2022, month=8, day=31, hour=18, minute=7, second=54,
+                                         microsecond=308543, nanosecond=321,
+                                        ).replace(tzinfo=pytz.FixedOffset(180)),
+            'msgpack': (b'\x4a\x79\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xb4\x00\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=180})",
+        },
+        'datetime_offset_convert': {
+            'python': tarantool.Datetime(year=2022, month=8, day=31, hour=16, minute=7, second=54,
+                                         microsecond=308543, nanosecond=321,
+                                         tzinfo=pytz.FixedOffset(60)).tz_convert(pytz.FixedOffset(180)),
+            'msgpack': (b'\x4a\x79\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xb4\x00\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=180})",
+        },
+        'datetime_offset_astimezone': {
+            'python': tarantool.Datetime(year=2022, month=8, day=31, hour=16, minute=7, second=54,
+                                         microsecond=308543, nanosecond=321,
+                                         tzinfo=pytz.FixedOffset(60)).astimezone(pytz.FixedOffset(180)),
+            'msgpack': (b'\x4a\x79\x0f\x63\x00\x00\x00\x00\x59\xff\x63\x12\xb4\x00\x00\x00'),
+            'tarantool': r"datetime.new({year=2022, month=8, day=31, hour=18, min=7, sec=54, " +
+                         r"nsec=308543321, tzoffset=180})",
+        },
     }
 
     def test_datetime_msgpack_decode(self):